1. Field of the Invention
The present invention relates to a hologram display employing a transparent hologram element as a screen to display images projected from a projector.
2. Description of the Related Art
A transparent hologram screen of a hologram display is known which is attached to, for example, a show window to display moving and still images projected from a projector for advertising or any other purposes. The projector is installed at an upper part or a lower part behind the screen. The screen diffracts and scatters light from the projector toward viewers so that the viewers may see images.
The conventional hologram displays, however, have some problems as follows.
One problem is that the hologram screen provides a peak efficiency in a specific wavelength area in the spectral distribution curve thereof.
As a result, reproduced light from the hologram screen intensely shows a color corresponding to the peak efficiency in the spectral distribution. Namely, the reproduced light from the hologram screen is tinged with the color corresponding to the peak wavelength area, and therefore, reproduced colors on the hologram screen are different from original colors contained in the light projected from the projector.
When the projected light contains halftone colors such as a flesh color, the peak-wavelength color conspicuously affects them.
To solve this problem, it is possible to employ a technique of making a hologram screen by multiple exposures. The hologram screen made by multiple exposures shows a uniform spectral distribution curve having at least two peaks in visible wavelengths ranging from 380 nm to 780 nm.
Multiple exposures, however, take a long time and, therefore, are unsuitable for mass production.